1. Technical Field of the Invention
The present invention relates to an audio signal processing apparatus and an audio signal processing method for processing of the waveform of a digital audio signal, and in particular, to the processing to improve quality of an audio signal to be replayed.
2. Related Art
Recently, in the field of digital audio, to replay audio signals of music or others recorded in recording mediums including discs, such as CD (Compact Disc) and MD (Mini Disc), and magnetic tapes, has become popular. On the other hand, replaying such audio signals by executing software installed in PCs (Personal Computers) has frequently been carried out as well.
Further, an audio signal compressed with a variety of compression formats, represented by MP3 (MPEG layer 3), is also often replayed with PCs. Such audio signal is also frequently replayed with a portable-dedicated player that has a semiconductor memory of which capacity is relatively small.
In the field of audio other than hi-fi audio, devices, such as cellular phones, PHSs, internet phones, and audio recorders employing semiconductor memories, are used to transmit/receive and replay digital audio signals compressed at lower bit rates.
In cases digital audio data are replayed by various devices, transmitted/received on communication, and stored in memories, reducing the size of data to be handled is of great advantage to cost and applications. It is therefore desired that amounts of data be reduced. Thus, it is normal that compressed digital audio data are stored in memories or transmitted through lines or wireless. Because the compression of the data is forced to cause deterioration of audio quality, it has been demanded to improve the deterioration when being used for hi-fi audio. When taking into account that PCs and portable replaying devices are also used to replay such digital audio signals, processing required to improve audio quality should be limited to processing on software and it is required for the current CPU to perform the processing in real time.
This demand, that is, replaying audio data in excellent audio quality, is raised as well in the field of audio other than hi-fi audio, in which portable devices such as cellular phones are used, particularly when audio data are compressed at lower transfer rates.